Protein O-GlcNAcase

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Protein O-GlcNAcase
Cartoon Image of OGA.jpg
Identifiers
EC number3.2.1.169
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum

Protein O-GlcNAcase (EC 3.2.1.169, OGA, glycoside hydrolase O-GlcNAcase, O-GlcNAcase, BtGH84, O-GlcNAc hydrolase) is an enzyme with systematic name (protein)-3-O-(N-acetyl-D-glucosaminyl)-L-serine/threonine N-acetylglucosaminyl hydrolase.[1][2][3][4][5] This enzyme catalyses the following chemical reaction

  1. [protein]-3-O-(N-acetyl-beta-D-glucosaminyl)-L-serine + H2O ⇌ [protein]-L-serine + N-acetyl-D-glucosamine
  2. [protein]-3-O-(N-acetyl-beta-D-glucosaminyl)-L-threonine + H2O ⇌ [protein]-L-threonine + N-acetyl-D-glucosamine

Isoforms[edit]

There are three isoforms of O-GlcNAcase in humans that have been identified. Full-length O-GlcNAcase (fOGA), the shortest O-GlcNAcase (sOGA), and a variant of OGA (vOGA). The human OGA gene is capable of producing two separate transcriptions, each capable of encoding a different OGA isoform. The long isoform gene codes for fOGA, a bifunctional enzyme that primarily resides in the cytoplasm. In contrast, vOGA resides within the nucleus. However, all three isoforms exhibit glycoside hydrolase activity.[6]

Homologs[edit]

Protein O-GlcNAcases belong to glycoside hydrolase family 84 of the carbohydrate active enzyme classification.[7] Homologs exist in other species as O-GlcNAcase is conserved in higher eukaryotic species. In a pairwise alignment, humans share 55% homology with Drosophilia and 43% with C. elegans. Drosophilia and C. elegans share 43% homology. Among mammals, the OGA sequence is even more highly conserved. The mouse and the human have 97.8% homology. However, OGA does not share significant homology with other proteins. However, short stretches of ~200 amino acids in OGA have homology with some proteins such as hyaluronidase, a putative acetyltransferase, eukaryotic translation elongation factor-1γ, and the 11-1 polypeptide.[8]

Reaction[edit]

Protein O-GlcNAcylation[edit]

Metabolic pathway for OGA

O-GlcNAcylation is a form of glycosylation, the site-specific enzymatic addition of saccharides to proteins and lipids. This form of glycosylation is with O-linked β-N-acetylglucosamine or beta-O-linked 2-acetamido-2-deoxy-d-glycopyranose (O-GlcNAc). In this form, a single sugar (β-N-acetylglucosamine) is added to serine and threonine residues of nuclear or cytoplasmic proteins. Two conserved enzymes control this glycosylation of serine and threonine: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). While OGT catalyzes the addition of O-GlcNAc to serine and threonine, OGA catalyzes the hydrolytic cleavage of O-GlcNAc from post-transitionally modified proteins.[9]

OGA is a member of the family of hexosaminidases. However, unlike lysosomal hexosaminidases, OGA activity is the highest at neutral pH (~7) and it localizes mainly to the cytosol. OGA and OGT are synthesized from two conserved genes (OGA is encoded by MGEA5) and are expressed throughout the human body with high levels in the brain and pancreas. The products of O-GlcNAc and the process itself plays a role in embryonic development, brain activity, hormone production, and a myriad of other activities.[10][11]

Over 600 proteins are targets for O-GlcNAcylation. While the functional effects of O-GlcNAc modification is not fully known, it is known that O-GlcNAc modification impacts many cellular activities such as lipid/carbohydrate metabolism and hexosamine biosynthesis. Modified proteins may modulate various downstream signaling pathways by influencing transcription and proteomic activities.[12]

Mechanism and Inhibition[edit]

a. Inhibitors for OGA b. Cross section of active site

OGA catalyzes O-GlcNAc hydrolysis via an oxazoline reaction intermediate.[13] Stable compounds which mimic the reaction intermediate can act as selective enzyme inhibitors. Thiazoline derivatives of GlcNAc can be used as a reaction intermediate. An example of this includes Thiamet-G as shown on the right. A second form of inhibition can occur from the mimicry of the transition state. The GlcNAcstatin family of inhibitors exploit this mechanism in order to inhibit OGA activity. For both types of inhibitors, OGA can be selected apart from the generic lysosomal hexosaminidases by elongating the C2 substituent in their chemical structure. This takes advantage of a deep pocket in OGA's active site that allow it to bind analogs of GlcNAc.[14]

There is potential for regulation of O-GlcNAcase for the treatment of Alzheimer's disease. When the tau protein in the brain is hyperphosphorylated, neurofibrillary tangles form, which are a pathological hallmark for neurodegenerative diseases such as Alzheimer's disease. In order to treat this condition, OGA is targeted by inhibitors such as Thiamet-G in order to prevent O-GlcNAc from being removed from tau, which assists in preventing tau from becoming phosphorylated.[15]

3-Dimensional structures[edit]

X-ray structures are available for a range of O-GlcNAcase proteins. The X-ray structure of human O-GlcNAcase in complex with Thiamet-G identified the structural basis of enzyme inhibition.[16]

References[edit]

  1. ^ Wells L, Gao Y, Mahoney JA, Vosseller K, Chen C, Rosen A, Hart GW (January 2002). "Dynamic O-glycosylation of nuclear and cytosolic proteins: further characterization of the nucleocytoplasmic beta-N-acetylglucosaminidase, O-GlcNAcase". The Journal of Biological Chemistry. 277 (3): 1755–61. doi:10.1074/jbc.M109656200. PMID 11788610.
  2. ^ Cetinbaş N, Macauley MS, Stubbs KA, Drapala R, Vocadlo DJ (March 2006). "Identification of Asp174 and Asp175 as the key catalytic residues of human O-GlcNAcase by functional analysis of site-directed mutants". Biochemistry. 45 (11): 3835–44. doi:10.1021/bi052370b. PMID 16533067.
  3. ^ Dennis RJ, Taylor EJ, Macauley MS, Stubbs KA, Turkenburg JP, Hart SJ, Black GN, Vocadlo DJ, Davies GJ (April 2006). "Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity". Nature Structural & Molecular Biology. 13 (4): 365–71. doi:10.1038/nsmb1079. PMID 16565725.
  4. ^ Kim EJ, Kang DO, Love DC, Hanover JA (June 2006). "Enzymatic characterization of O-GlcNAcase isoforms using a fluorogenic GlcNAc substrate". Carbohydrate Research. 341 (8): 971–82. doi:10.1016/j.carres.2006.03.004. PMID 16584714.
  5. ^ Dong DL, Hart GW (July 1994). "Purification and characterization of an O-GlcNAc selective N-acetyl-beta-D-glucosaminidase from rat spleen cytosol". The Journal of Biological Chemistry. 269 (30): 19321–30. PMID 8034696.
  6. ^ Li J, Huang CL, Zhang LW, Lin L, Li ZH, Zhang FW, Wang P (July 2010). "Isoforms of human O-GlcNAcase show distinct catalytic efficiencies". Biochemistry. Biokhimiia. 75 (7): 938–43. doi:10.1134/S0006297910070175. PMID 20673219.
  7. ^ Greig, Ian; Vocadlo, David. "Glycoside Hydrolase Family 84". Cazypedia. Retrieved 28 March 2017.
  8. ^ Gao Y, Wells L, Comer FI, Parker GJ, Hart GW (March 2001). "Dynamic O-glycosylation of nuclear and cytosolic proteins: cloning and characterization of a neutral, cytosolic beta-N-acetylglucosaminidase from human brain". The Journal of Biological Chemistry. 276 (13): 9838–45. doi:10.1074/jbc.M010420200. PMID 11148210.
  9. ^ Lima VV, Rigsby CS, Hardy DM, Webb RC, Tostes RC (2009). "O-GlcNAcylation: a novel post-translational mechanism to alter vascular cellular signaling in health and disease: focus on hypertension". Journal of the American Society of Hypertension. 3 (6): 374–87. doi:10.1016/j.jash.2009.09.004. PMC 3022480. PMID 20409980.
  10. ^ Förster S, Welleford AS, Triplett JC, Sultana R, Schmitz B, Butterfield DA (September 2014). "Increased O-GlcNAc levels correlate with decreased O-GlcNAcase levels in Alzheimer disease brain". Biochimica et Biophysica Acta. 1842 (9): 1333–9. doi:10.1016/j.bbadis.2014.05.014. PMID 24859566.
  11. ^ Shafi R, Iyer SP, Ellies LG, O'Donnell N, Marek KW, Chui D, Hart GW, Marth JD (May 2000). "The O-GlcNAc transferase gene resides on the X chromosome and is essential for embryonic stem cell viability and mouse ontogeny". Proceedings of the National Academy of Sciences of the United States of America. 97 (11): 5735–9. doi:10.1073/pnas.100471497. PMC 18502. PMID 10801981.
  12. ^ Love DC, Ghosh S, Mondoux MA, Fukushige T, Wang P, Wilson MA, Iser WB, Wolkow CA, Krause MW, Hanover JA (April 2010). "Dynamic O-GlcNAc cycling at promoters of Caenorhabditis elegans genes regulating longevity, stress, and immunity". Proceedings of the National Academy of Sciences of the United States of America. 107 (16): 7413–8. doi:10.1073/pnas.0911857107. PMC 2867743. PMID 20368426.
  13. ^ Dennis RJ, Taylor EJ, Macauley MS, Stubbs KA, Turkenburg JP, Hart SJ, Black GN, Vocadlo DJ, Davies GJ (April 2006). "Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity". Nature Structural & Molecular Biology. 13 (4): 365–71. doi:10.1038/nsmb1079. PMID 16565725.
  14. ^ Alonso J, Schimpl M, van Aalten DM (December 2014). "O-GlcNAcase: promiscuous hexosaminidase or key regulator of O-GlcNAc signaling?". The Journal of Biological Chemistry. 289 (50): 34433–9. doi:10.1074/jbc.R114.609198. PMC 4263850. PMID 25336650.
  15. ^ Lim S, Haque MM, Nam G, Ryoo N, Rhim H, Kim YK (August 2015). "Monitoring of Intracellular Tau Aggregation Regulated by OGA/OGT Inhibitors". International Journal of Molecular Sciences. 16 (9): 20212–24. doi:10.3390/ijms160920212. PMC 4613198. PMID 26343633.
  16. ^ Roth C, Chan S, Offen WA, Hemsworth GR, Willems LI, King DT, Varghese V, Britton R, Vocadlo DJ, Davies GJ (June 2017). "Structural and functional insight into human O-GlcNAcase". Nature Chemical Biology. 13 (6): 610–612. doi:10.1038/nchembio.2358. PMID 28346405.

External links[edit]